The present invention relates to a methodology and apparatus for rapid tissue decalcification and fixation employing a microwave (xe2x80x9cMWxe2x80x9d) oven with variable adjustable low wattage, a specialized tissue handling device and external reagent temperature control to gain the maximum benefit of MW irradiation without the heating problems associated with other MW methods.
Clinical and research analysis of tissue samples is an ongoing science. Bone tissue samples require that the calcium be removed prior to sectioning of tissue for microscopic analysis. In prior art it is known that MW irradiation of tissue samples will accelerate the process of decalcification and fixation when compared to routinely accepted bench tissue specimen processing methods. Prior art methods immerse a tissue sample in a reagent in a container placed in a MW oven. Prior art reagents include fixatives, acids, and chelators, as well as mixtures of those reagents. Prior art has demonstrated that use of corrosive acids must be carefully monitored and controlled to avoid tissue specimen destruction. Known MW irradiation methods require reagent changes for each one of multiple runs of the MW process. In prior art, elevated temperatures are commonly used for each cycle. Using prior art, MW-assisted/temperature-based processing methods have required these multiple reagent changes and a temperature control between 37xc2x0 C. and 45xc2x0 C. to maintain best sample quality, although prior art also demonstrates use of much higher temperatures. It has been demonstrated in prior art that temperatures above 45xc2x0 C. have accelerated the process further, but also has demonstrated tissue damage at those temperatures. Temperature control, by whatever means, is done by turning the magnetron on and off at an uncontrolled rate to maintain a preset temperature maximum. Using this known approach, the amount of MW energy applied to the sample will vary from run to run. These MW assisted methods, by necessity, rely on a temperature maximum or restriction that is above the ambient temperature to insure that the magnetron would activate and produce microwaves.
Time savings in processing samples will have a direct effect on surgical and clinical pathology, drug development and basic research in a wide range of fields from veterinary to human medicine and clinical pathology as well as research in medicine and the pharmaceutical industry. Reduction in times when using MW processing over established room temperature methods have been reported to be from 10 to 100 fold.
What is needed is a decalcification and fixation methodology that: 1) Utilizes a range of wattage between 50 w and 750 w MW processing; 2) uses a reagent circulation system as opposed to a static immersion system; 3) uses non-corrosive reagents; and 4) creates time saving as addressed above while producing quality and consistent results. The present invention addresses each of these needs.
The main aspect of the present invention is to provide an improved method for decalcification and fixation of mineralized samples utilizing apparatus consisting of off-the-shelf components that control all processing variables.
Another aspect of the present invention is to provide standardization of the described process across the clinical and research community.
Another aspect of the present invention is to provide a MW-assisted method not relying on MW heating as a component of the process but consisting of a continuous MW energy during the entire process.
Another aspect of the present invention is to provide for adjustment of the wattage output of the MW oven to optimize tissue decalcification and fixation turn-around time.
Another aspect of the present invention is to provide a system that, for the first time, controls all processing parameters in the decalcification and fixation of tissue. Such parameters include the amount of MW irradiation, wattage, temperature, time, etc.
Another aspect of the present invention is to provide for the control of all processing variables associated with previously published MW decalcification and fixation methods and test their validity.
Another aspect of the present invention is to increase productivity by reducing tissue sample turn around time in all settings while producing excellent processing results.
Another aspect of the present invention is to provide for a processing method utilizing commonly accepted reagents.
Another aspect of the present invention is to gain a rapid turn around time formerly dependent on the use of corrosive acids by substituting EDTA (ethylenediamine tetraacetic acid) and formalin in a MW environment.
Another aspect of the present invention is to provide an identifiable tissue specimen cassette and a cassette holder (tissue handling device) for holding tissue specimen cassettes in place during processing.
Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
The present invention provides rapid decalcification and fixation of mineralized tissues. The process utilizes a MW oven, which has adjustable wattage output to maintain operation within a narrow set of parameters. Tissue handling and identification with this system can be accomplished by standardized methods combined with a specialized containment device that is both solvent resistant and MW transparent. A MW oven operating at 2.45 GHz was used in the preferred embodiment of the present invention.
Further aspects of the system of the present invention are the variable wattage processing parameters that can be employed, for the first time, in the decalcification and fixation of tissue samples.
The present invention can increase productivity in all settings described and is anticipated to produce excellent processing results when ethylenediamine tetraacetic acid (EDTA) and 10% neutral buffered formalin are combined. EDTA is known to preserve tissue ultrastructure when the decalcification process is accelerated in the MW. Other reagents can be used, some of which are described below.
Further aspects of the present invention speak directly to the problems associated with other MW methods. The invention provides for the control of all processing variables associated with previously published MW decalcification methods. The present invention also suggests a non-thermal MW effect as a processing variable in simultaneous decalcification and fixation procedures.
The present invention utilizes a methodology for decalcification and fixation using off-the-shelf apparatus that consists (but not limited to) the following hardware apparatus and processing methodology:
A. Use of MW oven with a continuous power output range from 50 w to 750 w. Magnetron power settings are adjustable within a narrow range (typically +/xe2x88x9225 w) and maintain internal temperature control to about +/xe2x88x920.5xc2x0 C.
B. Use of a wide range of reagents such as EDTA and formalin (or others as acceptable).
C. Use of off-the-shelf hardware processing apparatus such as (but not limited to):
a. MW oven (see above) with adjustments for continuous power outputs of approximately 50 w to 750 w, time, temperature, monitoring probe, and input/output ports for external reagent circulation channels, and processing time control settings between about 1 sec and 100 hours.
b. An external recirculation device for continuous reagent recirculation, mixing, agitation, and temperature control which has both heat and cooling capabilities for the circulating reagent in order to maintain constant temperature, within narrow limits, of the reagent being circulated through a tissue handling device. The external recirculation device has an input and an output hose with a duplex pump to recirculate the reagent as it is being heated or cooled.
c. An internal MW oven processing bath into which is placed a tissue handling device.
d. A removable tissue handling device, which contains tissue(s) enclosed in histology tissue cassettes for decalcification and fixation.
e. A lid for the tissue handling device, which has one hole for a temperature probe.
f. An internal MW oven over-fill safety tray to capture any reagent spillage.
g. Utilization of anti-siphon and flow control devices to maintain a uniform reagent level within the tissue handling device to insure that tissue samples are continuously under reagent throughout the process.
h. Utilization of tissue histology cassettes capable of holding tissue samples and capable of being inserted into the tissue handling device.
i. Histology cassette tissue specimen holder, which is placed into the tissue handling device to secure and identify individual mineralized tissues.
j. Temperature probe inserted through the lid hole of the tissue handling device and into reagent contained within the tissue handling device. The temperature probe is used for monitoring and recording of the processing reagent temperature and can be used as a secondary reagent temperature control in case of any failure in the temperature control of the recirculation apparatus.
k. Use of materials that are both MW transparent and solvent resistant for the aforementioned trays, lids, handling devices, cassettes, tubing, etc. The materials used can be PTFE, polypropylene, polyethylene, silicone or similar materials.
l. Other components as required.
The above components and reagents, when used with the methodology of the present invention, will insure fixation and decalcification of the tissue samples at temperatures in the range of approximately 5xc2x0 C. to 45xc2x0 C. via continuous MW irradiation during the process. The results will show significant time savings exceeding 90% over routine processing methods and will be able (with accumulated tissue processing history) to result in one-step automatic processing of tissue samples for fixation and decalcification.
Typical specifications for a bath circulator are as follows:
A) Refrigeration and Heating System
1. Recirculation Temperature Range: xe2x88x9225xc2x0 C. to 150xc2x0 C.
2. Cooling Capacity: 500 watts at 20xc2x0 C. reagent temp.
3. Temperature Stability: +/xe2x88x920.01xc2x0 C.
4. Heater Wattage: 2000 watts
B) Pumping System
1. Pump Flow: 15 liters per minute max.
2. Pump Pressure: 0.5 bar (16xe2x80x2 head) max.
3. Pump type: Force and suction
C) General Specifications
1. Seamless stainless steel reservoir for easy cleaning and excellent reagent compatibility.
2. Reservoir drain for efficient reagent changes.
3. Wetted materials: Stainless steel, or other non-corrosive materials.
4. Reservoir Volume: 7 liters (1.9 gallons)
5. Unit dimensions: Approximately 60 cmxc3x9724 cmxc3x9745 cm.
6. Certifications: UL, CSA, CE Mark as required.
The non-uniform sample heating attributed to prior MW processes is not relevant with the present invention due to the volume and depth of reagent required within the MW cavity. Prior art has demonstrated that uneven sample heating, due to the presence of hot and cold spots within the MW cavity, can be greatly mitigated through the external recirculation and cooling of a similar reagent volume. Prior art also demonstrates that MW-assisted formalin fixation is a wattage dependent, not temperature dependent, process.
The combination MW-assisted decalcification and fixation will produce faster turnaround times. This outcome will facilitate: 1) diagnostic evaluation of surgical or clinical specimens; 2) faster treatment; 3) more efficient drug development and testing schedules; and 4) less wasted time in basic research for veterinary or human medicine.
The present invention outlines a methodology and apparatus, for the first time, that replaces MW-mediated sample temperature control with an external means based on the recirculation and cooling and/or heating of the processing reagent to maintain a constant temperature within the MW environment. This change makes the standardization of MW assisted processing a reality for the first time through the control of all of the processing variables (duration of MW sample exposure, wattage, temperature, time, sample processing environment). The key variable covered by the present invention is the ability to provide continuous MW energy between 50 w and 750 w for any time period between 1 second and 100 hours.
The present invention is the first to accelerate the fixation and decalcification processes using classical reagents: 10% neutral buffered formalin and EDTA that do not adversely affect sample quality. The use of 10% neutral buffered formalin is the standard fixative used in surgical and clinical pathology. EDTA, buffered or not, has been shown to preserve the structural integrity of tissues when used for decalcification. The aforementioned reagents are basically well known and widely used within clinical and surgical pathology. Other combinations of fixatives are known to work in combination with EDTA in a MW environment (unpublished research). Other decalcification reagents such as formic acid-based reagents, nitric acid-based reagents, hydrochloric acid-based reagents, sulphuric acid-based reagents, acetic acid-based reagents and mixtures of those reagents as well as proprietary reagents (e.g. Decal(copyright), Decal Stat(copyright), Formical-2000(copyright), Immunocal(copyright)) and fixatives such as zinc formalin, glutaraldehyde, paraformaldehyde, glyoxal, alcohol, acetone and proprietary reagents (e.g. Prefer, Preserve(trademark)) can also be used.
The present invention provides rapid processing including the ability to do an overnight process, without attendance by a technician. Only end point testing for decalcification would require technician intervention. Thus this process improves current tissue sample turnaround times for the processing of calcified tissues while at the same time provides standardization of the process throughout the clinical and research community.
Tissue handling and identification with the system of the present invention can be accomplished by standardized methods combined with a specialized containment device that is both solvent resistant and MW transparent. The specialized containment device, combined with a reagent container inside the MW, insures that the samples will remain covered by the processing reagent continuously throughout the process of decalcification and fixation. Anti-siphon and flow control devices included as part of the system, as well as the container design used inside the MW cavity insure the samples remain covered with the circulating reagent.
Further aspects of the system of the present invention are the low wattage processing parameters that can be employed, for the first time, in the decalcification and fixation of tissue samples. The continuous movement of the processing reagent around the samples is also a component of the described process. The recirculation device specified must be capable of maintaining a temperature within the specification of the MW maximum wattage used. The recirculation device should be one with push-pull recirculation capabilities for both heating and cooling of the reagent, as required.
The present invention can increase productivity in all settings described and is anticipated to produce excellent processing results when ethylenediamine tetraacetic acid (EDTA) and 10% neutral buffered formalin are combined. EDTA is known to preserve tissue ultrastructure when the decalcification process is accelerated in the MW.
Further aspects of the present invention speak directly to the problems associated with other MW methods. The invention provides for the control of all processing variables associated with previously published MW decalcification methods. The present invention establishes a MW effect as a processing variable in simultaneous decalcification and fixation procedures. The fixation process will be complete prior to decalcification.
The individual steps in the methodology of the present invention are described below in FIGS. 2A, 2B.